The process of picking cotton and thereafter removing seeds, trash and other foreign materials from the seed cotton is well known and understood by those familiar with the art. After seed cotton is harvested, it is then transported from the field to a cotton ginning facility. This facility has apparatus for receiving the seed cotton, drying and cleaning the seed cotton, removing the seeds from the cotton fiber or lint, cleaning the lint, and pressing the lint into bales for transport to warehousing, and later sold, commonly processing into yarn, thread, and fabric.
It is important to note that seed cotton is normally conveyed pneumatically through much of the drying process with many systems including more than one stage in the drying process. Another point to consider is whether the conveying air is of a positive pressure, a negative pressure, or some combination of the two. Those familiar in the art commonly refer to positive pressure systems as push systems, and negative pressure systems as pull systems or pull-through systems.
It is well understood cotton can be processed more easily and safely at certain levels of humidity, or moisture content. It is also well understood by those skilled in the art that the exchange of moisture into or out of seed cotton is promoted when there is a relative movement between the seed cotton and the heated conveying air.
Early in the mechanical stages used in the type of cotton ginning facility wherein the present invention might be useful is a device known as a rock trap or rock catcher, which separates rocks, green cotton bolls, and heavy foreign material from the pneumatically conveyed seed cotton as seen in FIG. 1. As seen in FIG. 1, the seed cotton is pneumatically conveyed through a conduit to an area where this separation is traditionally achieved with a hopper-type rock trap 10 which operates by abruptly expanding the cross-sectional area of the conduit and thus the negative-pressure conveying air stream and placing a deflector panel 11 in the direct path of the seed cotton and hot air stream. The deflector panel 11 directs the rocks and other heavy matter downward to an air-lock 12 and out of the system. Most of the seed cotton is light enough to be picked back up by the negative-pressure air stream as it passes around the deflector panel 11, and is then accelerated back into a conduit of similar cross-sectional area as was employed before the seed cotton entered the rock trap 10. A relatively small amount of seed cotton does not get picked back up by the hot air stream and falls down toward the air-lock. The air-lock is commonly either of a rotary design 13 or of a double-door design 14, with one door 14a separated by a small chamber over another door 14b where only one door opens at a time. Those in the industry often refer to rotary air locks as either vacuum droppers or vacuum wheels.
In an effort to minimize the amount of seed cotton lost in this process, an adjustable air inlet 15 is employed allowing ambient, cold air to reclaim the seed cotton and send it upward away from the air-lock and back into the conveying air stream. Energy is lost in this process in multiple ways. First the deflector panel creates a significant pressure drop; secondly the ambient air introduced to reclaim lost seed cotton dilutes the heat of the conveying air, thus reducing the drying capacity, and finally the energy required to pull in and accelerate this ambient air creates yet another pressure drop.
It must be acknowledged that in an effort to reduce the losses at the hopper-type rock trap, an innovative system was successfully developed wherein a secondary hot air stream was introduced immediately after the deflector to keep the conveying air warm and introduce additional turbulence to enhance the drying process. This approach was applied in many installations and helped improve the system efficiency, but all of the other losses described above remained. This approach also introduced the need for additional ductwork and complexity regarding air-balance, and introduced the opportunity for compromising the conveying air stream velocity by virtue of the pull air coming in through the secondary hot air stream inlet at the rock trap. That is to say, the air intake at the secondary inlet can reduce the effectiveness of the upstream air flow by reducing the pressure differential upstream of the rock trap.
FIG. 2 shows another type of rock trap known generically as a conveyor-belt suction-duct-type 20 which can be employed at the point where the seed cotton initially enters the air stream. In the better versions of this arrangement, hot air is pulled into a plenum chamber integrated into the suction-duct. In worst cases, the cotton is picked up with ambient air much like a large vacuum cleaner and almost immediately dropped into an elevated feed hopper without the benefit of any heating at all, thus adding to the overall system energy requirements. In the former case, ambient air is also pulled into the system, thus diluting the hot conveying air in such a way as to normally be less efficient than the previously described hopper-type rock trap 10.
While the number and type of components in drying systems vary from one facility to the next, some common system components can be seen in FIG. 3 and FIG. 4. It is not uncommon for the device following the rock trap to be either a shelf-type tower dryer 30 as taught by Bennett in U.S. Pat. No. 2,189,099 or some other type of large vessel 40 as taught by Jackson in U.S. Pat. No. 4,845,860, with either being designed to slow down the velocity of the seed cotton and allow slippage of the hot conveying air over and through the seed cotton. In many cases there is a necessary change in elevation between the outlet of the rock trap 10 and the inlet of the dryer. As a result, the ductwork between these two devices commonly contain at least two or three elbows 41 and some straight sections 42, each creating additional pressure drops.
It should also be noted the rock traps described above all operate primarily in drying systems using a negative pressure conveying air stream, or pull-through designs. By virtue of the need for the introduction of the reclaiming air above the air-lock, these systems do not easily lend themselves to positive pressure conveyance, or push designs.